Unassuming, media-shy and, as yet, unproven, Jay Y. Lee is the unofficial heir-apparent to lead Samsung Electronics Co Ltd, as the world's biggest technology group by sales approaches a crossroads after years of explosive growth.

The only son of Samsung's frail 72-year-old chairman Lee Kun-hee, Jay has been groomed for years to take over the sprawling South Korean family-run "chaebol", a conglomerate with interests spanning technology and insurance to shipbuilding and construction. Samsung Group's 2012 revenue of 380 trillion won ($371 billion) was more than a quarter of South Korea's nominal GDP.

The younger Lee, 45, became Samsung's vice chairman in 2012 after a spell as chief operating officer in what appeared to be a well choreographed long-term succession plan. But his father's ill-health - Lee senior was hospitalized for a heart attack at the weekend - has raised concerns over whether Jay is ready to take control.

"(Our) vice chairman is a strategic thinker and is very tenacious," said a senior Samsung executive, who didn't want to be named as he's not authorised to talk to the media. "He's been doing things that senior executives can't easily resolve on their own. For example, he spends a lot of time meeting key clients and then manages to cut a deal that would seem almost impossible."

"We've actually benefited significantly from his deal brokering and strategic decision making. He's been doing far more than what many people outside Samsung might guess. He's been learning for years from the chairman and has already been deeply involved in daily operations."

MEETING PEOPLE

Fluent in English and Japanese and dubbed the "Crown Prince of Samsung" by local media, Jay Lee has become the public face of Samsung in recent years, at meetings with corporate leaders, and politicians from China and the United States, building relationships for a group which had been regarded as secretive.

When South Korea's president invited Google Inc CEO Larry Page to visit Seoul a year ago, one of the first to meet him was Lee, who flew Page to a display plant south of the Korean capital to show off the latest technology Samsung was working on, including flexible screens that could potentially be fitted to Google Glass wearable devices.

The two firms haven't signed a deal on supplying bendy screens, but have since agreed global patent cross-licensing in a joint attack against Apple Inc - defying speculation of fraying ties as Samsung, the biggest smartphone maker using